Press wheel design for dry soils
FOR GOOD crop establishment in dry soil conditions - like in WA in 2000, 2001 and 2002 - not just any press wheels will do! At several meetings I have heard the comment, "We used one of those new fancy seeders with wide press wheels on our football club crop in dry conditions, and it didn't germinate as well as the knifepoint seeder without press wheels but with harrows, sown lap for lap."
Two important aspects of seeding that aid crop emergence are:
- seeds need to be pressed into firm undisturbed soil; and
- loose soil needs to be placed over the firmed seed.
Dwayne Beck calls these 'buffalo one' and 'buffalo two' (B1 and B2), being the natural action of buffaloes running across the US plains. Achieving B1 or B2 is not possible with wide press wheels, as they do not push the seed into firm, undisturbed soil, and they can't place loose soil over the seed. Wide press wheels firm a large area of soil over the seed. This causes more evaporation in the furrow than is possible with loose soil because of stronger capillary rise (see diagram 1 below).
So let's compare some more common systems for their effectiveness at Bland B2. Knife-point sowing, with harrows, does not push seed into firm soil (B1), but at least it puts loose soil over the seed (B2). Perhaps the best opener, in drying conditions, is the ConservaPak. This opener has an excellent B1, though its B2 ability is not always perfect. Canola establishment in dry soil at Meckering this year has been excellent with the ConservaPak.
The DBS opener, and knife-point openers with narrow press wheels, have a reasonably effective B1. They also often create a quite good B2. This is where the soil falls in from the sides of the vertical trench created by the press wheels (see diagram 2 below). V-shaped press wheels are not as effective as more vertical ones. This is because their weight is taken by the sides of the furrow, making it hard for them to press the seed, and they tend to firm the sides of the furrow, not allowing loose soil to fall in.
Double discs have an excellent B I, and often have stubble as an effective B2 in WA, although in some conditions, such as with grazed and wet stubble, there can be some emergence problems from hair-pinning. In fact, in wet conditions, it would be desirable to not use press wheels at all- or at least be able to back off their pressure. This is a problem with flat and wide press wheels where the whole weight of the seeder is taken by the press wheels.
Snake chains - for poor B2 seeders
If you have a system that gives no loose soil over the press wheels, then ' snake chains' (as Amjad of the Dept of Agriculture, Esperance WA, calls them) will help. These are chains that drag behind each opener, about 40 cm long with a large loop on the end. Farmers have been using them with good effect for many years.
Their main purpose is to tickle the sides of the presswheeled furrows to bring loose soil back into the furrow (B2). They may also help pull some trifluralin into the furrow without the extra weed stimulation that might occur with harrows.
* Excerpted from Snippets. WANTFA Farming Systems